1. Field of the Invention
This invention relates generally to processes and apparatus employing solids to provide the source of heat for chemical reaction. More specifically, the invention relates to the treatment of particulate solids used as the heat source to thermally crack hydrocarbons into olefins and to generate fuel gas coincident with the treatment of the particulate solids. The invention is particularly well adapted for use in an apparatus and process for use in the Thermal Regenerative Cracking (TRC) process, as described in U.S. Pat. No. 4,061,562 to McKinney et al and U.S. Pat. No. 4,097,363 to McKinney et al.
2. Description of the Prior Art
The use of solids in contact with gaseous or vaporized streams to effect a chemical reaction has long been in practice. The existing systems use both solids which participate in the reaction as catalyst or inert solids which provide the heat required for an endothermic reaction. Inert solids are used in fluidized bed reactors and in tubular reactors wherein solid-gas contact occurs in pneumatic flow.
In the prior art systems in which particulate solids are used to provide the heat required for reaction, coke is deposited on the particulate solids during the reaction. The coke is removed from the particulate solids during the combustion of fuel to provide the heat necessary for the reaction. The fuel used in the combustion step to heat the particulate solids is burned to a flue gas. Typically the fuel is burned with a high ratio of CO.sub.2 to CO in the presence of excess oxygen and the coke deposited on the particulate solids is burned and discharged as flue gas.
The combustion step occurs in fluid beds with relatively low gas velocities such as 3 feet per second. As a result, large diameter vessels are required for the combustion step. Customarily, the vessels have inside diameters of up to forty feet. In addition, the conventional large combustion vessels must be supported well above grade; i.e. 100 to 200 feet above grade.